On a Windows Server 2012 R2 with 2 NIC's with 2 static public and valid IP's, I'm trying to run Windows Routing and Remote Access Service and SoftEther side by side each on one NIC.

This is due to need for both PPTP and L2TP/IPSec connections on this server.

Each one of services work perfect when the other service is stopped, but when both are enabled (SoftEther VPN Server Service and Routing and Remote Access Service) clients of second running service fail to connect. However, no other service on both NIC's get affected (IIS, TCP messaging, file server, etc.)

I guess this might be some sort of conflict but I can't figure it out. No entry on server's Event Viewer, no specific error description except Cannot connect error 720 on PPTP clients and Error code 1 on SoftEther clients.

I have medium knowledge on networking so I appreciate any help or clue on where to look and how to solve this problem.

Regards

PS. SoftEther client can connect only when PPTP VPN on that PC is connected!
PS2. I just found out that when Routing and Remote Access Service is enabled the second NIC status is changed to Down and Non-Operational and it's unpingable.